The present invention relates to compositions for the treatment of hair and, in particular, to hair treatment compositions having improved rinsing properties. The invention relates especially to depilatory compositions, but will also find application in perming compositions.
Depilatory compositions are conventionally applied to the skin in the form of a cream, lotion, gel or mousse. After a period of time, the depilatory composition is removed by suitable means, such as by the use of a spatula. The active depilatory ingredient of the composition is conventionally an alkali metal salt or alkaline earth metal salt of an alpha or beta mercapto-carboxylic acid, such as potassium or calcium thioglycolate. These materials act by penetrating the hair and destroying the cystine bonds between the hair molecules. This weakens the hair to such an extent that the action of scraping and wiping away the depilatory composition causes the hair to break off at skin level, so that the hair may be removed.
A particular problem with compositions of this type is that the composition is difficult to remove completely from the skin and cannot be removed easily by simply rinsing away the composition. A heavy or vigorous mechanical scrubbing or scraping action is required, for example with a spatula, which can be a cause of considerable discomfort and inconvenience. Accordingly, the present invention seeks to provide hair treatment compositions, in particular depilatory compositions, having improved rinsing properties.
For conventional depilatory compositions in the form of a cream, lotion, gel or mousse, the emulsion is normally stabilized by including a relatively high amount of thickener in the composition. For example, conventional thickeners, which will be well known to those skilled in the art, are generally present at levels of up to 30% w/w. Alternatively, depilatory creams, lotions and gels can be formulated to give a stable emulsion by including high levels of fatty materials in the depilatory composition. In such compositions, either no thickener is present, or a small amount of thickener may be present.
In both cases, however, good rinsability of the depilatory composition from the skin will not be achieved. In the case where a high level of thickener is present, there will be such strong steric interactions between the polymeric materials in the emulsion that it is not possible to remove the depilatory composition quickly and easily from the skin by the mechanical action of water together with a light rubbing action. Where high levels of fatty materials are present, the texture or "body" of the depilatory composition will be too strong to allow the composition to be rinsed simply from the skin.
For example, International Patent Publication Ser. No. WO 93/08791 (The Boots Company PLC) describes depilatory formulations including, inter alia, smectite or kaolin clays such as bentonite. The clays are said to improve the feel of the depilatory composition on the skin and to reduce the unpleasant smell associated with the depilatory agent. However, the compositions described in WO 93/08791 would not have the improved rinsability of the depilatory compositions of the present invention. That is, the compositions described in WO 93/08791, containing the levels of thickeners and fatty materials as specified, would not be able to be rinsed simply from the skin by the mechanical action of water together with a light rubbing action.
However, in accordance with the present invention, we have found that it is possible to formulate a depilatory composition which is sufficiently stable to provide a good depilatory product, but which has weak enough steric interactions between the polymeric materials in the composition to provide improved rinsing properties.